Pliable covers for truck bodies, containers, or trailers serve both to protect a load within the body and to minimize the likelihood of all or part of the load from escaping from the body. Because covers for truck bodies are often large and unwieldy, some form of mechanical assistance is useful to spread and secure the cover over the truck body. Truck cover manipulators provide this assistance.
A truck cover manipulator assembly, such as shown in U.S. Pat. No. 4,050,734 to Richard, uses two metal arms powered by a drive mechanism to draw the flexible cover over the body from one end to the other. As the arms move longitudinally, the arm ends securing one end of the cover move in an arcuate path. When the arms are vertical, they raise the effective height of the truck considerably. Even when an operator is aware that the arms will extend upward, their exact height and amount of obstacle clearance are difficult to estimate visually. This situation is particularly hazardous when a truck cover manipulator assembly is operated near overhead power lines, because the arms of the truck cover manipulator assembly have the potential to contact the power lines and electrocute the operator or damage the truck.
In addition to the risk of electrocution, as the arms swing up and over the body, the upper portion of the arms are susceptible to bending from the load upon them or from striking an object. Furthermore, as the truck cover rises up with the arms, the truck cover may be caught by the wind, thereby inhibiting proper operation of the system or causing damage to it. In certain confined areas, such as in tunnels or under bridges, it is not possible to operate this type of manipulator assembly at all.
One solution for problems associated with truck cover support arms raising high above the body is taught in U.S. Pat. No. 4,874,196 to Goldstein et al. Goldstein teaches attachment of pivoting telescopic arms and actuators near the midpoint of a container for drawing a cover across the container in a low trajectory. Other truck cover manipulators such as U.S. Pat. Nos. 3,964,781 to Fenton; 4,023,857 to Killion; and 3,041,104 to Richard teach substantially horizontal deployment and retraction of a cover over an open body using tracks, guide-rails, or cables integrated with the body to help guide and anchor the cover.
Because the prior art truck cover assemblies are permanently attached to their bodies, their use is not economical in a trucking operation which uses roll-off container bodies, nor do they offer the possibility of an easily installed and detached manipulator comprising a single self-contained assembly. Furthermore, arms mounted at the midpoint of a body, whether projecting outward from the body or not, are not well protected from being struck and are therefore easily damaged.